Acoustic instrument



Oct. 15, 1929. H. J. ROUND ACOUSTIC INSTRUMENT Filed July 1925 M In 3 5 m. 37 6 5 0 10 Y I l A n 1 a. /f/%@ 12 z. z 1 9 2 2% 8 9 Fig. 5

HENRY JO$EPH ROUND 3& 144.5 flbtmlmu j'mi Patented 0a. 15, 1929' UNITED STATES- PATENTWOFFICE HENRY JOSEPH ROUND, OF MUSWELL HILL; LONDON, ENGLAND, ASSIGNOR '10 RADIO CORYOBATION OF AMERICA, A CORPORATION OF DELAWARE ACOUSTIC INSTRUMENT Application filed July 1, 1925, Serial No. 40,743, and in Great Britain July 16, 1924.

This invention relates to the diaphragms of acoustic instruments, whether such instruments are acted upon by sound waves to produce electric currents, or are vibrated to produce sound waves.

According to this invention a diaphragm of very thin light material is rigidly clamped in a case made very heavy in comparison with the weight of the diaphragm, and is damped over the whole, or substantially the whole, of its surface on one side, by contact with sponge rubber or the like, preferably smeared with thick oil on the surface in contact with the diaphragm.

The material of which the diaphragm is formed may be metallic or non-metallic, according to the use to which it is to be put.

If no magnetic properties are required in the diaphragm, I preferably make it of an aluminum alloy or of brass; a non-metallic diaphragm I preferably make of mica.

The diaphragm may be circular, stripshaped or annular, and is preferably such that it has a middle period of 800 to 1500 per second.

I have found that the best average results are obtained if the diaphragm is so arranged that the period when the damping is attached is about 1500' per second, and in order to obtain this, the diaphragm should have a slightly higher period before the oiled rubber is applied.

1 have also found that a diaphragm made rigid by forming it as a cone can be substituted for the stretched diaphragm, and in this case the attachment to the centre of a carbon button or a moving coil or the like is more easily effected without interfering with the natural vibration of the system.

Preferably the damping comprises oiled sponge rubber or oiled material such as felt applied to the diaphragm chiefly over the centre of the area, where possible, between the cone tip and the ring holder. It is, however, not essential to carry the damping completely up to the cone tip or to the edge of the cone, as the motions there are small. The diaphragm should be heavily clamped round the edge and can be of metal or somerigid material, such as paper treated with a phenol condensation product.

A diaphragm as described above can readily be made practically above audible frequency, when about 1 inch in diameter.

In the accompanying drawings which illustrate the invention, Figures 1 and 2 show in longitudinal section and front elevation respectively a microphone of the varying resistance type; Figure 3 shows a modification thereof; Figure 4 shows a magnetophone or telephone of the moving coil type; Figure 5 shows a modification of the apparatus shown in Figure 4; Figure 6 shows a magnetophone or telephone of the so-called Bell type, and Figure 7 shows a further modification of the apparatus shown in Figure 4.

Referring more particularly to Figures 1 and 2, 1 is a thin, light diaphragm, firmly clamped between the cylindrical parts 2, 2'

of a heavy body or casing. 3 is a cup containing a varying resistance material, such as finely divided carbon. The cup is provided on its edge with a felt or like washer 4 and is held lightly in contact with the central part of one side of the diaphragm by means of a bridge piece 5 within which the stem 6 of the cup can be adjusted and clamped in the desired position by a set screw 7. 8 is an oil soaked rubber sponge or the like which is contained within the body or casing and is in contact with substantially the whole area of the diaphragm. The sponge 8 is held within the casing by a base plate 9. The bridge piece 5 is insulated from the main body part 2 by insulating pieces 10. 11 are contact plugs or pins which are mounted in insulating blocks 12, and connected electrically one with the main body part 2 and the other with the cup 3. If the diaphragm 1 be made of a metal such as brass, it is preferably gold plated on the side in contact with the carbon in the cup 3. The diaphragm is preferably so stretched and proportioned that, in the relatively undamped state, it

' 1 exposed to 2', are preferably so dimensioned as to leave a considerable annular area of the diaphragm the action of the sound waves.

Figure 3 shows a microphone similar to that shown in Figures 1 and 2, except that the diaphragm 1 is conical. This diaphragm may conveniently be of metal or of stiff material, such as paper treated with a phenol condensation product, a suitable contact surface being arran ed for.

In Figure 4, which shows the invention applied to a magnetophone or telephone of the moving coil type, the diaphragm 1 is thin and light and carries a coil 13 mounted upon an annular former 14 attached to the diaphragm and projecting into the air gaps of a. magnetic circuit 15, which is magneti'zed-by a coil 16, or may be of the permanent magnet type. The diaphragm is clamped firmly at .its periphery by means 7 of a ring 17 and is damped over substanrubber material 8, such as sponge, felt or the like.

It will be apparent that such an arrangement will effect a very even and smooth damping since the oil tends to provide full contact between the rubber or felt and the diaphragm. 1

Figure 5 shows an arrangement similar to that illustrated by Figure 4, except that the diaphragm 1 is conical in form.

Figure 6 shows a so-called Bell type of magnetophone or telephone. The diaphragm 1 is clamped at its periphery between the parts 2 of the main body or casing and is actuated by or actuates an energizing unit of the usual Bell type, comprising a magnet core 18 and coils '1'9.

Figure 7 shows a further modification of the apparatus shown in Figure 4, the diaphragm being of the ring type.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is 1. In an acoustic device, a thin diaphragm mounted for vibration and means for damping the vibrations thereof comprising a body adjacent said dia hragm and a film of viscous material contacting the adjacent surfaces of said diaphragm and said body.

2. In an acoustic device, a thin diaphragm mounted for vibration and damping means comprising a porous body impregnated with oil and contacting one face of said body.

3. In an acoustic device, a diaphragm, damping means in contact with a surface of said diaphragm and a sound responsive device in contact with the diaphragm surface opposite the damping means.

4. A diaphragm adapted to vibrate by the action of sound waves impinging upon one of its surfaces and a device operated by the v b a ions f t p m, s c nta t wi h the surface .upon which the sound waves impinge. Y

5. In combination, a thin dia hragm adapted for rapid vibration, a ho low container mounted adjacent said diaphragm, a ring of yielding material contacting said diaphragm and the edge of said container which faces said diaphragm and a material of variable resistance within said container.

6. In an acoustic device, a frame, a diaphragm supported by said frame for free vibration, a hollow container having a projecting portion, adjustable clamping means carried by said frame and engaging said projecting portion whereby the position of said container relative to said diaphragm may be varied and a mass of material of variable resistance within said container.

7. In acoustic apparatus, a v1brat1on damper comprising a flexible absorbent material containing a liquid. tially'the whole of its under surface by oily In acoustic apparatus, a vibration damper comprising a flexible absorbent material substantially saturated with-oil.

9. A vibration'damper for acoustic apparatus comprising a flexible porous-material substantially saturated with a viscous liquid.

10. In combination, in an acoustic apparatus, a vibratory member, a stationary supporting member, and damping means for said vibratory member comprising a flexible absorbent material, containing a liquid interposed between said vibratory member and said supporting member.

11. .In acoustic apparatus, a device subject to vibration over a wide range of frequencies and means for damping such vibrations comprising a flexible absorbentmaterial substantially saturated with a li uid, said material being so placed with re erence to the vibrating member, that vibrations will cause movements of the liquid within the absorbent material.

' 12. An acoustic device subject to electromagnetic Vibrations over a wide range of frequencies within the acoustic frequency range, and means for damping said vibrations comprising a flexible absorbent material substantially saturated with a viscous oil and placed in contact with the vibrating parts and in the path of vibratory movement of said acoustic device.

13. The method of damping undesirable vibrations in acoustic apparatus which consists in causing the vibrating forces to be partially absorbed by forcing liquid through a plurality of minute capillary spaces.

14. In an acoustic device, a diaphragm,

damping means comprising a flexible, absorbent material containing a llquid, in con-' tact with a surface of said diaphragm, and a sound-responsive device in contact with the diaphragm surface opposite the damping means.

15. In a ous c d v c a d ap g HENRY JOSEPH ROUND. 

